Given below are five statements about levelling:
(A) In levelling, datum surface is an arbitrary surface with reference to which the elevations of the points are measured and compared.
(B) The line of collimation or the line of sight is the line joining the intersection of the cross-hairs to the optical centre of the object glass and its continuation.
(C) A foresight is the first staff reading taken after setting up the instrument in any position.
(D) The height of instrument is the elevation of the plane of collimation when the instrument is levelled.
(E) A change point indicates the shifting of the instrument, both back sight and intermediate sight are taken on this change point.
Choose the correct answer from the options given below: